Dynamic resistance measurement (DRM) is used for determining the overlap time of a circuit breaker. The overlap time is the time difference between the separation of the contacts in the rated current contact system and the separation of the contacts in the consumable or arcing contact system and indicates how severely the arcing contacts have already been eroded. It is therefore possible to assess the remaining life time of a quenching chamber. In the case of DRM, during CO operation (close, then open switch) a constant direct current of the order of magnitude of 1 kA is transmitted via the switch and the voltage drop across the switch is recorded. Recording of the voltage makes it possible to determine the line resistance of the switch at any point in time. Thus, the two times at which the contact systems open, and therefore also the overlap time, can be determined. The fact that the transmitted direct current needs to be so great is because the resistances of the two contact systems are very low in value and differ from one another only slightly. Only when a very high current is transmitted the voltage difference between the consumable contact system and the rated current contact system is within the measurable range.
One aspect of this method is the size of the required apparatus which in each case needs to be transported to the corresponding installation. In addition to the transportation costs for the service personnel, transportation costs also arise for the test apparatus. In order to make savings on these costs, there is interest in a smaller measuring device which measures the overlap time with, for example, the same degree of reliability as the previous one, but can be transported as hand luggage by service personnel.